The invention relates generally to an elbow weld joint and, more particularly to an apparatus and method for repairing or structurally replacing a core spray line elbow weld joint in a boiling water nuclear reactor.
A core spray piping system in operating boiling water reactors is typically of welded construction. The welds in the core spray system piping, however, are susceptible to intergranular stress corrosion cracking (IGSCC). As a consequence, the welded elbow joint in the core spray line can become cracked.
Common to most operating reactors, the core spray cooling water is delivered to the reactor core region by piping internal to the reactor vessel. A portion of this internal piping is a horizontal segment that follows the radius of curvature of the reactor vessel wall. An exemplary core spray line 2 is shown in FIG. 1. The proximal end of the horizontal piping is connected to a T-box at the core spray nozzle penetration. The distal end of this horizontal core spray line 2 is welded to a short radius elbow. The weld joining the distal end of the core spray line to the short radius elbow is designated as the P4a weld 4, and the weld joining the short radius elbow to the downcomer pipe 6 is designated as the P4b weld.
In the event that cracking should occur in the P4a weld, the structural integrity of the core spray line, which delivers cooling water to the reactor core, would be lost. A preemptive repair would be desirable to prevent separation of the P4a weld in the event that circumferential through-wall cracking should occur at this weld location in the core spray line.